Why would the Syrian Kurds even want independence? Especially as that means, in effect, bring swallowed by Iraqi Kurdistan.
Anyway the question is a bit nonsensical. Obviously a separatist will never be appeased by autonomy - the clue is in the name. But the idea that autonomy will automatically lead to separatist demands is definitely incorrect. There are plenty of autonomous little places - Aland, the Isle of Man, Channel Islands, the bulk of remnants of colonial empires etc. where autonomy and a regional identity have been established without demand for independence. Same with the Basques.
If the autonomous area is as rich or richer than the larger unit it's a part of, it can be stopped at autonomy. If they're poorer though, it will only make independence inevitable.